Power tools, such as electric drills and electric screwdrivers, commonly include a motor, a transmission mechanism and an output shaft. The motor includes a drive shaft. The drive shaft is used to drive the transmission mechanism so as to output power to the output shaft.
When these tools are operated as hand held power tools, a user needs to grip the tool with one or two hands. If the hand held power tools have a large size, obviously, they are not good to operate. So, hand held power tools are hoped not only to satisfy the requirements of torque, speed and power, but also have small size.
However, for currently known power tools, in order to obtain large output torque, the transmission mechanism commonly includes a multi-stage planet gear system. And in order to obtain different speeds, the transmission mechanism also includes a ring gear that is able to move up and down, which makes power tools have a large axial size and goes against the desire for miniaturization.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.